Excellent in moldability and productivity, thermoplastic resins have found their application in molding of a wide range of products such as electric and electronic parts, automobile parts, building materials, office supplies and the like, and the consumption of thermoplastic resin has been increasing year after year.
Ordinarily, a thermoplastic resin is molded into a desired shape by injection or extrusion molding. If the deposits, also known as the mold deposits, occur on the surface of the mold during the process, they are liable to be transferred to the surface of products, ruining the appearance of the products or leading to dimensional inaccuracy of the parts requiring highly accurate dimensions. Furthermore, if the mold deposits occur on the rugged mold surface processed by embossing, transferring of the ruggedness is significantly poor. These ruining of the appearance, deteriorating of the dimensional accuracy and poor transferring of the ruggedness may as well be caused by the residual anticorrosive agents, releasing agents, lubricants and the like.
In an effort to get rid of the effect of these residues, many molding processors clean the molds by dismantling them while consuming significant amount of time. In this way, the residues have been a big stumbling block against an attempt to improve productivity and reduce cost. Thus, traditionally, various detergents and cleaning methods for removing the residues from the molds have been proposed.
For example, JP-A-59-44205 describes a method for removing mold deposits in the process of molding polyoxymethylene by using a detergent composition comprising a benzyl alcohol and an aliphatic alcohol wherein the detergent is coated over the surface of the mold with a brush. JP-A-10-146844 describes a method for removing mold deposits with a solution comprising benzyl alcohol plus a solvent having at least one alcoholic hydroxyl group, wherein said solution is coated over the mold by spraying with the aid of a propellant. However, these detergents fail to exhibit a satisfactory cleaning effect depending upon the kind of molded resin used (for example, polyamide). Another problem is that they are governed by the organic rules of the Law for Industrial Safety and Health and the Regulations for Determining Work Environment in Japan. Under the circumstances, therefore, a detergent has been called for that has a cleaning method preferable in the work environment, which is less toxic and capable of being applied to a wider range of thermoplastic resins.
On the other hand, JP-A-61-238900, JP-A-61-76599, JP-A-5-186798, JP-A-11-92795 and the like disclose detergent compositions, in the role of aqueous detergents, containing limonene that have been used as perfume. These aqueous detergents have been found not to be always able to exhibit a satisfactory cleaning effect against oily deposits because the detergents alway contain approximately several % of water as the base. The aqueous detergents have been particularly poor in cleaning effect in the molds of the molding machine wherein a lot of oily deposits such as anticorrosive agent, lubricant, releasing agent and the like are lingering.
Furthermore, DE 3406500A1 discloses a detergent comprising limonene alone or limonene with N-methylpyrrolidone or the like added in a small amount and a method for removing residues on a mold after it is used to mold polyurethane, polystyrene and polyvinyl chloride, wherein said detergent is sprayed over the mold, allowed to work for 5 minutes, and then the residues are washed away with a halogenic solvent such as methylene chloride and the like. However, these methods also have the problem that they are not always able to exhibit a satisfactory cleaning effect, depending upon the kind of resin. When the molding of resin is restarted after the cleaning, a number of molding shots are required to stabilize the physical properties of the molded resin, resulting in poor efficiency. Furthermore, in the case where very intractable deposits have to be removed from the mold as a result of long continuous molding operations, the mere spraying of the detergents is not good enough. The mold is often immersed into a solution of detergents and cleaned by ultrasound. In such an event, these detergents take too long in dry wiping after the ultrasonic cleaning, giving rise to a problem of inefficiency.
Furthermore, JP-A-5-104539 discloses a detergent for a mold for resin molding work comprising an alcoholic organic solvent and a hydrocarbonaceous organic solvent. Herein, ethanol and propanol are used as the alcoholic organic solvent, while octane, xylene, kerosene and the like are used as the hydrocarbonaceous organic solvent. These detergents are capable of exhibiting a good effect in removing pollutants on a mold after the ordinary general-purpose resin is molded. However, their cleaning effect is not always satisfactory to remove deposits that are hardly removable if they occurr on the mold as a result of molding, for example, modified polyphenylenether (PPE) and the like, or to remove the likewise hardly removable deposits resulting from a very long time continuous molding of even the ordinary general-purpose resin such as acrylonitrile/butadiene/styrene (ABS) resin. Furthermore, the above-mentioned hydrocarbonaceous organic solvents are not always preferable from the viewpoint of the work environment.
Moreover, a mold detergent comprising limonene and isopropyl alcohol (tradename: SLIDE ON/CYCLE MOLD CLEANER, manufactured by SLIDE PRODUCTS, INC.) has been marketed in the U.S. The product, however, does not exhibit a good effect in removing the deposits depending upon a certain resin, and further isopropyl alcohol is not always preferable from the viewpoint of environment.
As described above, the detergents and cleaning methods answering the needs of market by combining the multiple excellent performances have not as yet been known. Certainly, the market has called for a detergent and a cleaning method capable of exhibiting the excellent removing effect against the deposits that are hardly dealt with by conventional detergents and methods, requiring a short span of time until the physical properties of the molded resin are stabilized when the molding is restarted after cleaning and being preferable from the viewpoint of work environment.